The subject of the present invention is a percussive hydraulic apparatus.
A percussive hydraulic apparatus comprises a body inside which there is mounted a cylinder in which there is guided an impact piston driven back and forth by an incompressible fluid and which strikes a tool held at the lower end of the body. The distribution of the fluid which moves the piston is performed by a distributor housed in a distribution box mounted in the body.
Document EP 0 638 013 relates to a percussive apparatus in which the cylinder of the impact piston and the various liners forming the cylinder guiding the latter and the distributor are held in a body by a top cover, itself fixed to the body by screws. These screws mechanically immobilize the various parts, but give rise to the following disadvantages:
the distribution of the pressure exerted by the cover is entirely dependent upon the clamping force transmitted by each screw. Now, tensioning short screws on a civil engineering works apparatus is generally performed by torquing, with all the uncertainties associated with this type of stressing: non-uniform friction in the threads of the screws, precision of the tightening equipment, etc. Deformation of the impact-piston guide assembly may therefore be caused by the tightening of the cover.
the cover cannot simultaneously be in contact with the liners and the body of the apparatus as the functional clearance needed might then cause the cover to bend and this would result in bending on the screws, which is detrimental to their fatigue strength.
a slight backing-off of the cover fixing screws results, through a relative movement of the liners with respect to one another, in wear of the bearing surfaces, and gradual misalignment which may detract from the hydraulic guidance of the impact piston.
The object of the invention is to provide a percussive hydraulic apparatus in which the various parts intended to be mounted in an enclosure of the body are not subjected to the constraints resulting from screw-tightening, with the ensuing disadvantages defined above.
To this end, the percussive hydraulic apparatus to which it relates comprising a body inside which there is mounted a cylinder in which there is guided an impact piston driven back and forth by an incompressible fluid and which strikes a tool held at the lower end of the body, the distribution of the fluid which moves the piston being performed by a distributor housed in a distribution box mounted in the body, is characterized in that the cylinder and the distribution box are entirely contained in the enclosure delimited by the body, in that the cylinder bears axially on the body, in that the distribution box is mounted coaxially with respect to the cylinder and bears mechanically thereon and in that the surfaces perpendicular to the axis of the apparatus, subjected to pressure, are arranged and dimensioned in such a way that the resultants of the hydraulic forces applied to the parts, cylinder and distribution box, are directed in the same direction toward a support situated in the body of the apparatus, throughout all the phases of the operating cycle thereof.
According to one embodiment, this apparatus also comprises a distribution cover arranged coaxially with respect to the distribution box and bearing axially thereon, of which the surfaces perpendicular to the axis of the apparatus and subjected to pressure are arranged and dimensioned in such a way that the resultant of the hydraulic forces applied to the cover is directed in the same direction as the resultant of the forces applied to the other parts, cylinder and distribution box, throughout all the phases of the operating cycle of the apparatus.
It is apparent from this structure that the parts which consist of the cylinder, the distribution box and the distribution cover are not fixed mechanically by the cover of the body, as they usually would be. The degree to which the cover is tightened down onto the body therefore has absolutely no influence on the integrity of the various parts inside the body, on the one hand, and relative to one another, on the other hand, because these parts are firmly pressed against one another and against the body by hydraulic forces. This results in the possibility of having far broader manufacturing tolerances than in the conventional case of assembly by screw-fastening, while at the same time enjoying better apparatus behavior since the risks of deformation of the cylinder and of misalignment of the guidance of the impact piston which are known from the prior art are avoided.
According to one feature of the invention, the support of the body, against which the various parts are hydraulically pushed, consists of the end wall of the enclosure, on the tool side, in which enclosure the cylinder is mounted.
According to another feature, each part, cylinder, distribution box, distribution cover, has two antagonist surfaces the first of which is subjected alternately to the high and to the low pressure and the second of which, of a larger surface area than the first, is constantly subjected to the high pressure.
According to one embodiment of this apparatus, the end face of the cylinder bearing against the end wall of the enclosure of the body is at atmospheric pressure while its opposite face is always subjected to the high pressure. The cylinder is thus firmly pressed into the end wall of the enclosure of the body.
According to one possibility, the distribution box has two successive cylindrical portions of which the one facing toward the piston is closed off by an end wall delimiting, with the piston, a chamber connected alternately to the high and to the low pressure, and of which the other portion, which has a larger cross section than the first, is situated in a chamber constantly supplied with high-pressure fluid.
Advantageously, the distribution cover has a circular wall the outer face of which bears against the interior face of the distribution box, the interior face of which serves, in part, to guide the distributor, the lower face of which delimits, in part, an annular chamber which is constantly connected to the low-pressure circuit, this circular wall ending in a part of larger cross section resting on the end of the distribution box and situated in a chamber constantly supplied with high-pressure fluid.
According to another embodiment, the distribution cover has a circular wall the outer face of which bears in a bore of the body, the lower face of which bears against the upper face of the distribution box, the interior face of which serves, in part, to guide the distributor and delimits therewith an annular chamber which is constantly connected to the low-pressure circuit, this circular wall ending, at its upper end, in a part of larger cross section situated in a chamber constantly supplied with high-pressure fluid.